The invention relates to improvements made to manufacturing machines for containers made of plastic material, such as flasks or bottles, by blow molding blanks. The blanks are, for example, premolded or intermediate containers obtained during a preliminary phase of processing the plastic material. In particular, the invention relates to a blow molding system and nozzles for use in a molding process.
The manufacturing of containers by blow molding blanks of plastic material is now well known. A blank or preform is obtained either by injection of the plastic material in an injection and forming mold, or by extrusion of the plastic material in a forming mold. The preform is then subjected to an appropriate thermal treatment, depending on the characteristics of the container to be obtained, and/or is placed in a finishing mold containing the shape of the container to be obtained. A nozzle is then introduced into the opening (the neck) of the preform and a blowing fluid, generally air under high pressure, is injected into the preform to inflate it and coat the walls of the mold with the material, thus making it possible to obtain the container. Preferably, particularly in the applicant""s machines that make containers using preforms that were previously injected, the blow molding is preceded or accompanied by drawing (or elongation) of the preform using an elongating rod. Again preferably, when the drawing precedes a blow molding process using high-pressure air, the drawing is accompanied by a premolding process using air at a lower pressure to avoid a condition where, especially at the time of drawing, the material does not contract onto the rod.
When the blank is an intermediate container, the intermediate container is generally obtained using a first container, the first container itself obtained by blow molding of a preform in a first mold. The first container, after it leaves the first mold, is subjected to specific processing, typically thermal, following which the intermediate container is obtained. The intermediate container is then placed in a second mold where the intermediate container is changed into the final container by injection of a blowing fluid using a nozzle identical to the one mentioned above.
European patents granted under the numbers 237459 and 442836, in the name of the applicant, describe two variations in the equipment that make it possible to obtain a first container using an injected preform, then, after changing the first container into an intermediate container, to obtain a final container with good mechanical properties. This is particularly so for containers filled at high temperature or filled with gaseous or carbonated drinks. Typically, the procedures and equipment for manufacturing the containers described above requires a phase where a single intermediate container is obtained. As such, it would be very easy to imagine obtaining several successive intermediate containers before obtaining the final container.
The molds used for the manufacture of final containers, or each mold for obtaining a container from which an intermediate container is obtained, are generally made of at least two parts which can be separated or moved close to each other. Each of these two parts has half the shape of the container to be obtained (e.g., base, wall, shoulder). Preferably, however, the known molds have three parts: one part with the shape of the base of the container, and two parts to make up the wall and shoulder of the container. This preferred structure makes mold release easy when the base of the container has certain types of relief patterns (particularly petal-shaped bases). The parts are separated and removed from each other when the blank is put in place and at the time the container is ejected. The parts are then moved close together, and the mold is closed during the blow molding phases (with or without drawing and/or premolding).
One disadvantage of the equipment or machines for manufacturing containers (intermediate or final) concerns the structure of the nozzles that are used. It is known that the neck of the final container is generally obtained at the time the preform is manufactured. When the preform is transformed into the container, either a final container or an intermediate container, the dimensions of the neck must not be changed or be changed only very little. Still and consequently, the dimensions of the neck of the intermediate container must not vary or can vary only little, and the final container must therefore have a neck identical to that of the preform. In fact, the neck has either threads for receiving a threaded cap or a reinforced edge for holding a crimped cap or a stopper. It is therefore very difficult to control the deformation of the neck after formation of the preform, and is thus preferable to keep the neck in the same condition after successive transformations.
It is for this reason that, at the time of processing the preform to the final or intermediate container and, in this latter case of an intermediate container into another container (intermediate again or final), the neck is supported on the outside of the mold and is not modified by the blow molding. The nozzle is made up of a tube on which the blow molding end (tip of the nozzle) is contracted so that it can be inserted into the opening of the blank. Typically, the end of the nozzle has the cross section of a truncated cone. The diameter at the base of the truncated cone, thus of the nozzle, is less than that of the opening. As a result, when the nozzle is introduced into the neck, contact ends up being established between the truncation of the cone and the interior peripheral edge of the lip of the preform, assuring seal integrity at the time of blow molding and keeping the blank in a good position with respect to the mold.
However, this type of nozzle is not completely appropriate because of the high pressures necessary for blow molding (typically 40 bars in the machines of the applicant). Because of the high pressures, it is necessary to exercise a significant support pressure between the nozzle and the preform to avoid leaks. Thus, it is necessary that the neck has a material thickness significantly great to give it adequate rigidity so that it is not deformed by the nozzle at the time of the support. Still, the price of a container is largely connected with the cost of the material. As such, one trend that has developed recently is to obtain blanks with a reduced neck to reduce the cost price, but there is a lower limit below which the nozzle will cause the neck to burst.
Further, the same type of equipment can be used to manufacture a series of different containers. The user is sometimes required to modify the individual settings of his equipment. If the height of the neck is modified and/or if the diameter of the neck is modified, it is necessary to modify the regulation of the nozzle flow and/or possibly to change the nozzle. This results in a loss of time, which can add surcharge costs for using the manufacturing equipment. In addition, these nozzles are poorly adapted for blow molding of sterile or aseptic containers using a sterilizing or antiseptic fluid because of the contact zone between the interior of the neck and the nozzle. If the nozzle has not been sterilized before blow molding and it remains in this condition, septic or non-sterile particles may be found there and contaminate the interior of the container.
Also when a drawing rod is present, which is the rule, the drawing rod slides axially into the interior of a cylindrical opening in the nozzle and is oriented along the longitudinal axis of the latter, and a ring space is left open around the rod to permit the passage of the blowing fluid around the rod in this opening. But, the cross section of this space is necessarily limited in such a way that the passage of the fluid is slowed down.
The present invention seeks to overcome the aforementioned problems. According to the present invention, a nozzle is provided for carrying the blowing fluid into the interior of a blank supported below its neck in a blow molding mold, in such a way that the neck emerges from the mold, the nozzle having an opening for bringing the fluid into the blank is characterized in that the opening has dimensions such that when a blank is in place in the mold and the nozzle is in the blow molding position, the opening surrounds the neck and the peripheral edge of the opening opposite the blank making up the tip of the nozzle comes to rest on the mold and means for sealing are provided at the level of this support.
The nozzle according to the present invention thus makes it possible to eliminate all the problems mentioned above. In the nozzle of the present invention, there is no longer direct support on the blank to ensure sealing, so that reduced necks may be used. Also in the present invention, the problems connected with changes in settings in conventional nozzle devices are resolved. That is, it is enough to calibrate the opening in such a way that it can contain larger necks than the machine will be called upon to process. Further, since the blowing fluid arrives around the neck, the problems connected with antiseptics or sterilization are resolved. The blowing fluid also arrives around the neck in such a way that not only the interior of the container, but also the exterior of the neck is cleaned. In addition, if there is no drawing rod, a larger passage cross section is available to the blowing fluid since the tip of the nozzle is not on the interior but is on the exterior of the neck, which results in greater blow molding efficiency.
In a first variation of the present invention, sealing means are attached to the end of the nozzle tip. In a second variation, the sealing means are fastened on the installation mold to which the nozzle is connected.